1. Field of the Invention
This invention relates to a color liquid crystal display device comprising a color filter in a liquid crystal cell.
2. Description of the Prior Art
There are known various types of color display systems for liquid crystal display devices. For example, the DAP system utilizes the birefringence of liquid crystal molecules. According to the twisted nematic system, a color polarizer is employed as one of the polarizers, or a color filter is provided for a netural polarizer. The quest-host system employs a dichroic dye in a liquid crystal layer.
According to the DAP system, the inclination of liquid crystal molecules is controlled by application of an electric field, and various colors can be reproduced by the interference of light passing through a liquid crystal cell. The practical use of this system is, however, hindered by a number of factors, including the high level of technique which is required for controlling the cell thickness, and the dependence of the color on the viewing angle.
A system employing a color polarizer or a color filter is considerably better than the DAP system. The color of the display is not so influenced as in the case of the DAP by variation in the cell thickness. The dependence of the color on the viewing angle is considerably improved, and a multi-color display is easy to achieve by a single cell. There is no vagueness of color by parallax. The guest-host system is also substantially free from any problem such as cell thickness control, and the dependence of color on the viewing angle.
In a conventional color liquid crystal display device including a color filter in a liquid crystal cell, however, a layer of polyvinyl alcohol is employed for the orientation of liquid crystal molecules (The 28th Spring Meeting of Japan Society of Applied Physics -30a-Y-10). As polyvinyl alcohol is soluble in water, it is deteriorates, and fails to be capable of proper molecule orientation in the case of water invasion in the cell during a long time of use. The cell requires a complicated process for manufacture, and is costly, since a layer of polyvinyl alcohol has to be formed on a color filter.